63,344 research outputs found
Model Theory and Entailment Rules for RDF Containers, Collections and Reification
An RDF graph is, at its core, just a set of statements consisting of subjects, predicates and objects. Nevertheless, since its inception
practitioners have asked for richer data structures such as containers (for
open lists, sets and bags), collections (for closed lists) and reification (for
quoting and provenance). Though this desire has been addressed in the
RDF primer and RDF Schema specification, they are explicitely ignored
in its model theory. In this paper we formalize the intuitive semantics
(as suggested by the RDF primer, the RDF Schema and RDF semantics specifications) of these compound data structures by two orthogonal
extensions of the RDFS model theory (RDFCC for RDF containers and
collections, and RDFR for RDF reification). Second, we give a set of
entailment rules that is sound and complete for the RDFCC and RDFR
model theories. We show that complexity of RDFCC and RDFR entailment remains the same as that of simple RDF entailment
On the Complexity of Nonrecursive XQuery and Functional Query Languages on Complex Values
This paper studies the complexity of evaluating functional query languages
for complex values such as monad algebra and the recursion-free fragment of
XQuery.
We show that monad algebra with equality restricted to atomic values is
complete for the class TA[2^{O(n)}, O(n)] of problems solvable in linear
exponential time with a linear number of alternations. The monotone fragment of
monad algebra with atomic value equality but without negation is complete for
nondeterministic exponential time. For monad algebra with deep equality, we
establish TA[2^{O(n)}, O(n)] lower and exponential-space upper bounds.
Then we study a fragment of XQuery, Core XQuery, that seems to incorporate
all the features of a query language on complex values that are traditionally
deemed essential. A close connection between monad algebra on lists and Core
XQuery (with ``child'' as the only axis) is exhibited, and it is shown that
these languages are expressively equivalent up to representation issues. We
show that Core XQuery is just as hard as monad algebra w.r.t. combined
complexity, and that it is in TC0 if the query is assumed fixed.Comment: Long version of PODS 2005 pape
A note on total and list edge-colouring of graphs of tree-width 3
It is shown that Halin graphs are -edge-choosable and that graphs of
tree-width 3 are -edge-choosable and -total-colourable.Comment: arXiv admin note: substantial text overlap with arXiv:1504.0212
The Parameterised Complexity of List Problems on Graphs of Bounded Treewidth
We consider the parameterised complexity of several list problems on graphs,
with parameter treewidth or pathwidth. In particular, we show that List Edge
Chromatic Number and List Total Chromatic Number are fixed parameter tractable,
parameterised by treewidth, whereas List Hamilton Path is W[1]-hard, even
parameterised by pathwidth. These results resolve two open questions of
Fellows, Fomin, Lokshtanov, Rosamond, Saurabh, Szeider and Thomassen (2011).Comment: Author final version, to appear in Information and Computation.
Changes from previous version include improved literature references and
restructured proof in Section
Finding Dominators via Disjoint Set Union
The problem of finding dominators in a directed graph has many important
applications, notably in global optimization of computer code. Although linear
and near-linear-time algorithms exist, they use sophisticated data structures.
We develop an algorithm for finding dominators that uses only a "static tree"
disjoint set data structure in addition to simple lists and maps. The algorithm
runs in near-linear or linear time, depending on the implementation of the
disjoint set data structure. We give several versions of the algorithm,
including one that computes loop nesting information (needed in many kinds of
global code optimization) and that can be made self-certifying, so that the
correctness of the computed dominators is very easy to verify
Data Structures and Data Types in Object-Oriented Databases
The possibility of finding a static type system for object-oriented programming languages was initiated by Cardelli [Car88, CW85] who showed that it is possible to express the polymorphic nature of functions such a
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